Aqueous dispersion liquid and coating material, film, and product using the same

ABSTRACT

In one embodiment, an aqueous dispersion liquid contains at least one particles selected from tungsten oxide particles and tungsten oxide composite particles. A mean primary particle diameter (D50) of the particles is in the range of 1 nm to 400 nm. In the aqueous dispersion liquid, concentration of the particles is in the range of 0.1 mass % to 40 mass %, and pH is in the range of 1.5 to 6.5. The aqueous dispersion liquid excels in dispersibility of particles and capable of maintaining good liquidity for a long period.

CROSS-REFERENCE TO RELATED APPLICATION

This application is continuation of prior International Application No.PCT/JP2009/000984, filed on Mar. 4, 2009 which is based upon and claimsthe benefit of priority from Japanese Patent Application No.2008-054139, filed on Mar. 4, 2008 and No. 2008-106891, filed on Apr.16, 2008; the entire contents of all of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to an aqueous dispersionliquid and a coating material, a film, and a product using the same.

BACKGROUND

Tungsten oxide thin films are widely used as dielectric materials usedfor electronic devices such as capacitors, filters, and semiconductorchips, and the like, optical element materials used for opticalcommunication filters, isolators, and the like, electrochromic materialsused for light control mirrors, and the like, and gas chromic materialsused for gas sensors, and the like. Moreover, tungsten oxide is known tofunction as a visible light responsive photocatalyst material, and isattracting high attention in view of industrial application.Conventionally, the tungsten oxide thin films have been formed by avacuum deposition method, a sputtering method, a laser ablation method,a sol gel method, and the like.

JP-A 2001-152130 (KOKAI) describes a photocatalyst material obtained bysputter-depositing tungsten oxide on a substrate, where tungsten oxidehaving a triclinic crystal structure is mainly used. The sputterdeposition exposes a substrate to high temperatures, and thus it may benot applicable depending on the heat resistant temperature of thesubstrate. The sputter deposition is complicated in process managementor the like, and not only it becomes costly depending on the shape andsize of the substrate, but deposition on a wide area of a buildingmaterial or the like is difficult. A visible light responsivephotocatalyst layer formed of a sputter-deposited tungsten oxide film isexcellent in hydrophilicity, but has a problem that its decomposingperformance for harmful gas of acetaldehyde and the like isinsufficient. Hydrophilicity data under irradiation with visible lightare not provided, and thus it is presumed that sufficient photocatalyticperformance under visible light is not obtained.

Similarly to the sputtering method, the laser ablation method needs toheat a substrate to high temperatures for controlling crystallinity, andit may be not applicable depending on the heat resistant temperature ofthe substrate. Not only it becomes costly depending on the shape andsize of the substrate, but deposition on a wide area of a buildingmaterial or the like is difficult. Deposition of tungsten oxide by thesol gel method can be performed relatively inexpensively, butappropriate heating is needed for forming a tungsten oxide film withgood crystallinity. Thus, it has constraints on heat resistanttemperature of the substrate, shape of the substrate, and so on. When atungsten oxide film is used as a photocatalyst film which decomposesorganic gas or the like, it needs to have an appropriate crystalstructure and a large specific surface area, but the sol gel method isnot capable of controlling the crystal structure and the specificsurface area of the tungsten oxide sufficiently.

A photocatalyst film using a titanium oxide or the like is generallyformed by mixing a dispersion liquid obtained by dispersing titaniumoxide particles in a dispersion medium with an inorganic binder toprepare a coating material, and applying this coating material on asubstrate. The coating material can be applied on various substrates andfurther can be deposited at around room temperature by selecting abinder, and thus it is possible that the photocatalyst film isapplicable to a wide range of products. In the case of a coatingmaterial using a dispersion liquid of a photocatalyst powder, it isnecessary that particles are well dispersed in the film, for securingperformance of the photocatalyst and obtaining film properties of highstrength and smoothness. As a typical method to obtain a good dispersioncoating material, there is known a method to produce a dispersion liquidin which a photocatalyst powder is dispersed sufficiently in adispersion medium, and add a binder therein.

Aggregation can easily occur when ultra-fine particles are used like thetitanium oxide based photocatalyst, and it is needed to add a finishingagent or a dispersion agent for stabilizing the dispersion state.However, the finishing agent and the dispersion agent are factors tolimit photocatalytic performance, and efforts are made to decrease theamount of adding them as much as possible. For example, stabilization ofthe dispersion state by adding acid and decreasing pH is practiced.Further, lately, there are demands to decrease use amount of volatileorganic compounds (VOC) in view of environmental protection, and aqueousdispersion liquids and coating materials using no organic solvent areincreasing. Numerous non-ionic compounds are used as a dispersion agentin the aqueous dispersion liquids and coating materials.

When a film using the tungsten oxide powder is formed, first it isnecessary to generate fine tungsten oxide particles. As a method ofproducing a fine tungsten oxide powder, there is known a method to heatan ammonium paratungstate (APT) in the air to obtain a tungsten trioxidepowder (see JP-A 2002-293544 (KOKAI)). By the method heating APT in theair, a triclinic tungsten trioxide powder with a primary particlediameter of approximately 0.01 μm (BET specific surface area=82 m²/g) isobtained. For improving photocatalytic performance of the tungstentrioxide (WO₃) powder, it is needed to be in a stable particle state.

By applying disintegration processing, the tungsten trioxide powder canbe refined to a certain degree, but it is difficult to have a particlediameter of 100 nm or smaller for example, including aggregatedparticles. Moreover, when the disintegration processing is applied tomake a fine powder, the crystal structure of a fine tungsten trioxide(WO₃) powder changes by the stress of the disintegration processing.There occurs a defect to cause re-coupling of electrons and positiveholes by stress of the disintegration processing, and thus using it as aphotocatalyst conceivably causes decrease in performance. In theproduction method described in JP-A2002-293544 (KOKAI), kneading of 20hours or more is needed for stabilizing a BET specific surface area,which poses a problem of low production efficiency of the tungstentrioxide powder.

As a method for obtaining a fine powder efficiently, thermal plasmaprocessing is described in JP-A2006-102737 (KOKAI) for example. Byapplying the thermal plasma processing, a fine powder with a particlediameter of 1 nm to 200 nm is obtained. Besides the thermal plasmaprocessing, as processing methods capable of oxidizing a tungstenmaterial while sublimating it in an oxygen atmosphere, there are knownarc discharge processing, laser processing, electron ray processing, gasburner processing, and the like. However, when a fine tungsten oxidepowder produced by applying these methods is used as it is as aphotocatalyst, there may be a case where optical characteristics andcrystal structure are not optimum, and sufficient photocatalystcharacteristics cannot always be obtained. Therefore, for forming aphotocatalyst film, it is necessary to perform control to haveappropriate optical characteristics, crystal structure, and particlediameter in a powder state.

For forming a stable dispersion liquid using the tungsten oxideparticles, it is important not only to use tungsten oxide particles witha fine primary particle diameter, but also to facilitate decompositionof, for example, aggregated particles and prevent re-aggregation.However, under the current situation, a dispersion liquid and a coatingmaterial in which the tungsten oxide particles do not separate orprecipitate for a long period have not been obtained. Particularly, whenthe tungsten oxide particles are applied to a photocatalyst, thedispersion liquid and the finishing agent become a factor to limitphotocatalytic performance. Thus, a small amount of the dispersionliquid or the finishing agent is added, or a dispersion liquid to whichit is not necessary to add them is desired. However, sufficientperformance has not been obtained with such a dispersion liquid or acoating material.

DETAILED DESCRIPTION

In one embodiment, an aqueous dispersion liquid contains at least oneparticles selected from tungsten oxide particles and tungsten oxidecomposite particles. A mean primary particle diameter (D50) of theparticles is in a range of 1 nm to 400 nm, concentration of theparticles is in a range of 0.1 mass % to 40 mass %, and pH is in a rangeof 1.5 to 6.5.

In one embodiment, a coating material contains the aqueous dispersionliquid of the embodiment, and at least one binder component selectedfrom an inorganic binder and an organic binder. In one embodiment, afilm is formed by applying the aqueous dispersion liquid of theembodiment or the coating material of the embodiment on a substrate. Inone embodiment, a product includes a film of the embodiment.

An aqueous dispersion liquid according to an embodiment contains atleast one particles selected from tungsten oxide particles and tungstenoxide composite particles (hereinafter referred to as tungsten oxidebased particles). The tungsten oxide based particles contained in theaqueous dispersion liquid have a mean primary particle diameter (D50) inthe range of 1 nm to 400 nm. In the aqueous dispersion liquid,concentration of the tungsten oxide based particles is in the range of0.1 mass % to 40 mass %, and pH is in the range of 1.5 to 6.5. Theaqueous dispersion liquid is used for forming a covering film, a coatingfilm, or the like containing the tungsten oxide based particles.

The aqueous dispersion liquid is not limited to one such that tungstenoxide particles are dispersed in water, and may be one such thattungsten oxide composite particles are dispersed in water. The tungstenoxide composite is one such that tungsten oxide as a main constitutecontains a transition metal element and/or other metal elements. Thetransition metal element is an element with an atomic number from 21 to29, 39 to 47, 57 to 79, or 89 to 109. It is preferred that the tungstenoxide composite include at least one metal element selected from Ti, Zr,Mn, Fe, Pd, Pt, Cu, Ag, Al, and Ce.

It is preferred that the content of the metal element in the tungstenoxide composite be in the range of 0.001 mass % to 50 mass %. When thecontent of the metal element is more than 50 mass %, it is possible thatthe characteristics of the tungsten oxide particles decrease. It is morepreferred that the content of the metal element be 10 mass % or less.The lower limit value of the content of the metal element is notparticularly limited, but it is preferred that the content thereof be0.001 mass % or more, more preferably 0.01 mass % or more. For avoidingdecrease of dispersibility of the aqueous dispersion liquid, it ispreferred that the content and form of the metal element be adjusted soas not to cause a large change in pH and zeta potential. Consideringsuch points, it is preferred that the content of the metal element be 2mass % or less.

In the tungsten oxide composite used for the aqueous dispersion liquid,the metal element may exist in various forms. The tungsten oxidecomposite can include a metal element in the form of a single metalelement, a compound including a metal element (compound includingoxide), a complex compound of tungsten oxide, or the like. The metalelement included in the tungsten oxide composite may itself form acompound with other elements. An example of a typical form of the metalelement is oxide. The metal element is mixed with, for example, atungsten oxide powder in the form of a single element, a compound, acomplex compound, or the like. The metal element may be carried by thetungsten oxide.

The method of combining the tungsten oxide with the metal element(specifically a single element, a compound, or a complex compound of atleast one element selected from Ti, Zr, Mn, Fe, Pd, Pt, Cu, Ag, Al, andCe) is not particularly limited, and various combining methods such as amixing method to mix powders with each other, an impregnation method, acarrying method, and so on can be applied. A typical combining method isdescribed below. An example of a method of combining copper withtungsten oxide is a method to mix a tungsten oxide powder with a copperoxide powder. Another effective method is such that the tungsten oxidepowder is added and mixed in an aqueous solution of copper nitrate orcopper sulfate or in an ethanol solution, dried thereafter totemperatures from 70° C. to 80° C., and burned at temperatures from 500°C. to 550° C.

Further, it is also possible to apply a method to disperse a tungstenoxide powder in an aqueous copper chloride solution or an aqueous coppersulfate solution, and dry this dispersion liquid (impregnation method).The impregnation method is not limited to a method of combining copper,and can be applied to a method of combining iron using an aqueous ironchloride solution, a method of combining silver using an aqueous silverchloride solution, a method of combining platinum using an aqueousplatinum chloride solution, a method of combining palladium using anaqueous palladium chloride solution, and the like. Moreover, tungstenoxide may be combined with a metal element (oxide) using an oxide solsuch as a titanium oxide sol or an alumina sol. Besides them, variouscombining methods can be applied.

It is preferred that the tungsten oxide based particles used for theaqueous dispersion liquid be in a state of having a stable crystalstructure. If the crystal structure is unstable, when the aqueousdispersion liquid is stored for a long period, it is possible that thecrystal structure of the tungsten oxide based particles changes, andthereby its liquidity changes and dispersion state decreases.Furthermore, the tungsten oxide based particles may contain metalelements or the like as a minute amount of impurity. It is preferredthat the content of metal elements as impurity elements be 2 mass % orless. As the impurity metal elements, there are elements generallyincluded in a tungsten ore and contamination elements or the like whichare mixed in when a tungsten compound or the like used as a raw materialis produced, and examples include Fe, Mo, Mn, Cu, Ti, Al, Ca, Ni, Cr,Mg, and so on. It is not applicable when these elements are used ascomponent elements of a composite.

The mean primary particle diameter (D50) of the tungsten oxide basedparticles used for the aqueous dispersion liquid is in the range of 1 nmto 400 nm. It is preferred that a BET specific surface area of thetungsten oxide based particles be in the range of 4.1 m²/g to 820 m²/g.Particles before dispersion or particles resulted from drying adispersion liquid are estimated by SEM, TEM, or the like, and the meanprimary particle diameter (D50) is obtained based on a mean particlediameter (D50) of integrated diameters with reference to volumes ofparticles with n being 50 or more from an image analysis of a picture.The mean primary particle diameter (D50) may match the mean particlediameter converted from the specific surface area.

In order to generate a stable dispersion liquid to obtain a uniform film(a film containing the tungsten oxide based particles), it is betterthat the primary particle diameter is small and the specific surfacearea is large. Therefore, when the mean primary particle diameter of thetungsten oxide based particles is larger than 400 nm, or when the BETspecific surface area is smaller than 4.1 m²/g, it is not possible toobtain sufficient characteristics as a dispersion liquid. On the otherhand, when the mean primary particle diameter of the tungsten oxidebased particles is smaller than 1 nm or when the BET specific surfacearea is larger than 820 m²/g, the particles are too small and providepoor handleability as a powder. Therefore, practicability of the powderand the dispersion liquid using this powder decreases.

When the tungsten oxide based particles are used as a photocatalystpowder, generally the larger the specific surface area and the smallerthe particle diameter, the higher the performance of the photocatalystpowder. Therefore, when the mean primary particle diameter of thetungsten oxide based particles is larger than 400 nm or when the BETspecific surface area is smaller than 4.1 m²/g, the photocatalyticperformance of the tungsten oxide based particles decreases, and it isdifficult to form a uniform and stable film. The photocatalyticperformance decreases also in this point. When the mean primary particlediameter of the tungsten oxide based particles is too small, thedispersibility decreases and it is difficult to produce a uniformdispersion liquid.

It is preferred that the mean primary particle diameter of the tungstenoxide based particles be in the range of 2.7 nm to 75 nm, morepreferably in the range of 5.5 nm to 51 nm. It is preferred that the BETspecific surface area be in the range of 11 m²/g to 300 m²/g, morepreferably in the range of 16 m²/g to 150 m²/g. When the primaryparticle diameter of the tungsten oxide based particles is too small,the dispersibility decreases as described above. For improving thispoint, it is preferred that the mean primary particle diameter of thetungsten oxide based particles be 5.5 nm or larger.

The concentration of the tungsten oxide based particles in the aqueousdispersion liquid is in the range of 0.1 mass % to 40 mass %. When theconcentration is less than 0.1 mass, the content of the tungsten oxidebased particles is insufficient, and desired performance cannot beobtained. When the concentration is higher than 40 mass %, the tungstenoxide based particles exist in an adjacent state when they become afilm, and the surface area for exhibiting performance cannot beobtained. Accordingly, not only the sufficient performance cannot beexhibited, but also the cost is increased because the tungsten oxidebased particles are included more than necessary.

It is preferred that the concentration of the tungsten oxide basedparticles is in the range of 1 mass % to 20 mass %, more preferably inthe range of 1 mass % to 10 mass %. A high-concentration dispersionliquid containing the tungsten oxide based particles by 20 mass % ormore is capable of easily achieving a state that the tungsten oxidebased particles are uniformly dispersed when it is diluted to produce acoating material. It has an advantage that a coating material in whichthe tungsten oxide based particles are uniformly dispersed can beproduced.

Moreover, the pH of the aqueous dispersion liquid is in the range of 1.5to 6.5. In the aqueous dispersion liquid containing the tungsten oxidebased particles, the zeta potential is negative with pH being in therange of 1.5 to 6.5, and thus an excellent dispersed state can beachieved. Such a dispersion liquid and a coating material using thisliquid can be applied on a substrate or the like thinly without havingunevenness. The pH of the aqueous dispersion liquid has a correlationwith the concentration of the tungsten oxide based particles. Thedispersion state changes when the pH changes, and good dispersibility isobtained when pH is in the range of 1.5 to 6.5.

When the pH of the aqueous dispersion liquid is smaller than 1.5, thezeta potential gets close to zero, and thus the dispersibilitydecreases. When the pH of the aqueous dispersion liquid is larger than6.5, it becomes close to the alkaline side, and the tungsten oxidebecomes liable to dissolve. To adjust the pH of the aqueous dispersionliquid, an acid or alkaline solution of hydrochloric acid, sulfuricacid, tetramethylammonium hydroxide (TMAH), ammonia, sodium hydroxide,and the like may be added as necessary. It is preferred that the pH ofthe aqueous dispersion liquid be in the range of 2.0 to 6.0, morepreferably in the range of 2.5 to 5.5.

With the pH of the aqueous dispersion liquid being in the range of 2.5to 5.5, photocatalytic performance (gas decomposing performance) can beexhibited more effectively.

After the aqueous dispersion liquid having pH in the range of 2.5 to 5.5is applied and dried, when the surface state of particles is observed bya FT-IR (Fourier-transform infrared absorption spectroscopy), absorptionof hydroxyl can be seen in the vicinity of 3700 cm⁻¹. Using such a filmas a photocatalyst film, it is possible to obtain excellent organic gasdecomposing performance. When the aqueous dispersion liquid having pHadjusted to 6 is applied and dried, the absorption of hydroxyldecreases, and the gas decomposing performance decreases as well. Whenthe pH of the aqueous dispersion liquid is adjusted to 2, although thehydroxyl exists, the dispersibility slightly decreases due to that thezeta potential gets close to zero, and the gas decomposing performancedecreases slightly.

In the aqueous dispersion liquid of this embodiment, particle sizedistribution of the tungsten oxide based particles is preferably suchthat the D90 diameter is in the range of 0.01 μm to 10 μm. The aqueousdispersion liquid is produced by mixing particles with a dispersionmedium, and performing dispersion processing with an ultrasonicdispersion machine, a wet jet mill, a beads mill, or the like. In theaqueous dispersion liquid obtained in this manner, the tungsten oxidebased particles include aggregated particles, which are aggregatedprimary particles. The particle size distribution is measured with a wetlaser diffraction particle size distribution analyzer or the likeincluding the aggregated particles, and when the D90 diameter inintegrated diameters with reference to volumes is in the range of 0.01μm to 10 μm, a good distribution state and an even and stable filmformability can be obtained.

When the D90 diameter of the particle size distribution of the tungstenoxide based particles is smaller than 0.01 μm, the entire particle sizeof the tungsten oxide based particles is too small, and thus thedispersibility decreases. Accordingly, it becomes difficult to obtain auniform dispersion liquid or coating material. When the D90 diameter islarger than 10 μm, it becomes difficult to form a uniform and stablefilm. Particularly, when the tungsten oxide based particles have thephotocatalytic performance, it is not possible to exhibit thisphotocatalytic performance sufficiently.

It is preferred that the D90 diameter in the particle size distributionof the aqueous dispersion liquid be in the range of 0.01 μm to 1 μm,more preferably in the range of 0.01 μm to 0.1 μm. In order to form auniform and smooth film or a film with high strength, it is preferredthat the aggregated particles be disintegrated as much as possible tomake the D90 diameter smaller. When the tungsten oxide based particleshave the photocatalytic performance, for exhibiting the photocatalyticperformance after the film is formed, conditions not to give too muchdistortion to particles in the dispersion processing are set preferably.In order to form a uniform and stable film using an aqueous dispersionliquid or a coating material having good dispersibility, application bya method such as spin coating, dipping, spraying, or the like ispreferred.

When the color of the aqueous dispersion liquid is expressed by theL*a*b color system, it is preferred that the aqueous dispersion liquidhave a color in the range of a* of 10 or less, b* of −5 or more, and L*of 50 or more. By applying a dispersion liquid having such a color toneon a substrate and forming a film, good photocatalytic performance canbe obtained, and additionally, the color of the substrate will not beimpaired. Therefore, it becomes possible to obtain a coating material ora film.

The aqueous dispersion liquid of this embodiment may contain alcohol inthe range of 20 mass % or less as a dispersion medium other than water.As the alcohol, for example, methanol, ethanol, 1-propanol, 2-propanol,or the like is used. When the content of the alcohol is more than 20mass %, aggregation easily occurs. It is preferred that the content ofthe alcohol be 10 mass % or less. The aqueous dispersion liquid may besuch that the tungsten oxide based particles are dispersed in an aqueousdispersion medium in a state that they are mixed with, carried on, orimpregnated in a material having absorption performance such asactivated carbon, zeolite, or the like.

It is preferred that the tungsten oxide based particles (powder) usedfor the aqueous dispersion liquid in this embodiment be produced by thefollowing method, but it is not limited thereto. It is preferred thatthe tungsten oxide based particles be produced applying a sublimationprocess. Further, combining a heat treatment process with thesublimation process is also effective. With tungsten trioxide basedparticles produced by such a method, the above-described mean primaryparticle diameter, BET specific surface area, and crystal structure canbe achieved stably. Moreover, the mean primary particle diameterapproximates to the value converted from the BET specific surface area,and particles with small dispersion in particle diameter (fine powder)can be obtained stably.

The sublimation process will be described. The sublimation process is aprocess in which tungsten trioxide particles are obtained by sublimatinga metal tungsten powder, a tungsten compound powder, or a tungstencompound solution in an oxygen atmosphere. The sublimation is aphenomenon that a state change from a solid phase to a vapor phase, orfrom a vapor phase to a solid phase occurs without undergoing a liquidphase. The tungsten oxide powder can be obtained by oxidizing the metaltungsten powder, tungsten compound powder, or tungsten compound solutionas a raw material while sublimating it.

Any one of the metal tungsten powder, tungsten compound powder, and thetungsten compound solution may be used as the raw material (tungstenmaterial) in the sublimation process. Examples of the tungsten compoundused as the raw material include tungsten trioxide (WO₃), tungstendioxide (WO₂), tungsten oxide of a low-grade oxide or the like, tungstencarbide, ammonium tungstate, calcium tungstate, tungstic acid, and thelike.

By performing the sublimation process of the tungsten raw material asdescribed above in the oxygen atmosphere, the metal tungsten powder orthe tungsten compound powder is turned from a solid phase to a vaporphase instantly, and further the metal tungsten vapor turned to a vaporphase is oxidized, to thereby obtain tungsten oxide particles. Even whenthe solution is used, it turns to a vapor phase after being tungstenoxide or compound. Thus, the tungsten oxide particles can be obtainedusing oxidation reaction in a vapor phase. Moreover, the crystalstructure of the tungsten oxide particles can be controlled.

As the raw material for the sublimation process, preferably at least oneselected from a metal tungsten powder, a tungsten oxide powder, atungsten carbide powder, and an ammonium tungstate powder is used sincethe tungsten oxide particles obtained by sublimation in the oxygenatmosphere hardly include impurities. The metal tungsten powder and thetungsten oxide powder are preferred particularly as raw materials forthe sublimation process since they do not include any harmful by-product(substance other than the tungsten oxide) formed in the sublimationprocess.

As the tungsten compound used for the raw material, a compound includingtungsten (W) and oxygen (O) as its constituent elements is preferred.Including W and O as constituent elements makes it easy to be sublimatedinstantly when inductively-coupled plasma processing or the likedescribed later is applied in the sublimation process. Examples of sucha tungsten compound include WO₃, W₂₀O₅₈, W₁₈O₄₉, WO₂, and the like.Further, a solution, salt, or the like of tungstic acid, ammoniumparatungstate, or ammonium metatungstate, is also effective.

When the tungsten oxide composite particles are produced, a transitionmetal element or other elements may be mixed in the form of metal,compound including oxide, complex compound, or the like, in addition tothe tungsten material. By processing the tungsten oxide with otherelements at once, complex compound particles of complex oxide of thetungsten oxide and other elements, or the like can be obtained. Thetungsten oxide composite particles can also be obtained by mixing thetungsten oxide particles with or carrying them on single particles orcompound particles of other metal elements. The method of combining thetungsten oxide with other metal elements is not particularly limited,and it is possible to apply various publicly known methods.

It is preferred that the metal tungsten powder or the tungsten compoundpowder as the tungsten material have a mean particle diameter in therange of 0.1 μm to 100 μm. The mean particle diameter of the tungstenmaterial is more preferably in the range of 0.3 μm to 10 μm, furthermorepreferably in the range of 0.3 μm to 3 μm, desirably in the range of 0.3μm to 1.5 μm. When the metal tungsten powder or the tungsten compoundpowder having the mean particle diameter in the above ranges is used,sublimation occurs easily.

When the mean particle diameter of the tungsten material is smaller than0.1 μm, the raw material powder is too fine. Thus, pre-adjustment of theraw material powder becomes necessary, handleability decreases, andadditionally the cost increases, thereby making it unfavorable in anindustrial aspect. When the mean particle diameter of the tungstenmaterial is larger than 100 μm, uniform sublimation reaction does notoccur easily. Even when the mean particle diameter is large, processingwith a large energy amount can cause uniform sublimation reaction, butthis is unfavorable in an industrial aspect.

An example of the method of sublimating the tungsten material in theoxygen atmosphere in the sublimation process is at least one processingselected from inductively coupled plasma processing, arc dischargeprocessing, laser processing, electron beam processing, and gas burnerprocessing. Among them, in the laser processing or the electron beamprocessing, laser or electron beam is irradiated to perform thesublimation processing. The laser or electron beam has a smallirradiation spot diameter, and thus it takes time to process a largeamount of raw material at once. However, they have an advantage that itis not necessary to strictly control the particle diameter or stabilityof supply amount of the raw material powder.

The inductively coupled plasma processing or the arc dischargeprocessing needs adjustment of a generating area of plasma or arcdischarge, but it is capable of allowing oxidation reaction of a largeamount of raw material powder to occur at once in the oxygen atmosphere.Further, the amount of raw material to be processed at once can becontrolled. The gas burner processing needs a relatively low power cost,but it is difficult to process a large amount of raw material powder orraw material solution. Accordingly, the gas burner processing isinferior in productivity. In addition, the gas burner processing may beone having sufficient energy for causing sublimation, and is notparticularly limited. A propane gas burner, an acetylene gas burner, orthe like is used.

When the inductively coupled plasma processing is applied to thesublimation process, generally there is used a method in which plasma isgenerated using argon gas or oxygen gas, and the metal tungsten powderor the tungsten compound powder is supplied into this plasma. Examplesof the method of supplying the tungsten material into the plasma includea method to blow the metal tungsten powder or the tungsten compoundpowder together with carrier gas, a method to spray a dispersion liquidin which the metal tungsten powder or the tungsten compound powder isdispersed in a predetermined liquid dispersion medium.

Examples of the carrier gas used when the metal tungsten powder or thetungsten compound powder is blown into the plasma include air, oxygen,inert gas containing oxygen, and the like. Among them, the air is usedpreferably because of its low cost. When oxygen is contained enough inthe reaction field, like in the case where reaction gas including oxygenis supplied other than the carrier gas, the case where the tungstencompound powder is the tungsten trioxide, or the like, inert gas such asargon or helium may be used as the carrier gas. For the reaction gas,preferably oxygen, inert gas including oxygen, or the like is used. Whenthe inert gas including oxygen is used, preferably the oxygen amount isset so that it is possible to sufficiently supply a necessary oxygenamount for oxidation reaction.

By applying the method of blowing the metal tungsten powder or thetungsten compound powder together with carrier gas, and adjusting thegas flow rate or the pressure in a reaction container, the crystalstructure of the tungsten trioxide particles can be controlled easily.Specifically, it is easy to obtain tungsten trioxide particles having acrystal structure of at least one selected from monoclinic crystal andtriclinic crystal (monoclinic crystal, triclinic crystal, or mixedcrystal of monoclinic crystal and triclinic crystal) or one in whichrhombic crystal is mixed therewith. It is preferred that the crystalstructure of the tungsten trioxide particles be a mixed crystal ofmonoclinic crystal and triclinic crystal or a mixed crystal ofmonoclinic crystal, triclinic crystal, and rhombic crystal.

An example of the dispersion medium used for producing the dispersionliquid of the metal tungsten powder and the tungsten compound powder isa liquid dispersion medium having oxygen atoms in molecules. Using thedispersion liquid facilitates handling of the raw material powder. Asthe liquid dispersion medium having oxygen atoms in molecules, forexample, there is used one including at least one selected from waterand alcohol by 20 capacity % or more. As the alcohol used as the liquiddispersion medium, for example, at least one selected from methanol,ethanol, 1-propanol, and 2-propanol is preferred. Since water andalcohol easily evaporate by heat of plasma, they do not hindersublimation reaction or oxidation reaction of the raw material powder,and they easily facilitate oxidation reaction because they containoxygen in molecules.

When the metal tungsten powder or the tungsten compound powder isdispersed in the dispersion medium to produce the dispersion liquid, itis preferred that the metal tungsten powder or the tungsten compoundpowder be included in the range of 10 mass % to 95 mass %, morepreferably in the range of 40 mass % to 80 mass % in the dispersionliquid. By dispersing in the dispersion liquid in such a range, themetal tungsten powder or the tungsten compound powder can be disperseduniformly in the dispersion liquid. When it is dispersed uniformly,uniform sublimation reaction of the raw material powder can occureasily. When the content in the dispersion liquid is less than 10 mass%, the amount of the raw material powder is too small, and it cannot beproduced efficiently. When the content is more than 95 mass %, theamount of the dispersion liquid is small, the viscosity of the rawmaterial powder increases and makes it sticky to the container, and thusthe handleability decreases.

By applying the method to have the metal tungsten powder or the tungstencompound powder in the dispersion liquid and blowing it into plasma, thecrystal structure of the tungsten trioxide particles can be controlledeasily. Specifically, tungsten trioxide particles having a crystalstructure of at least one selected from monoclinic crystal and tricliniccrystal or one in which rhombic crystal is mixed therewith can beobtained easily. Further, also by using a tungsten compound solution asthe raw material, the sublimation reaction can be performed uniformly,and moreover, controllability of the crystal structure of the tungstentrioxide particles improves. The method using the dispersion liquid asdescribed above is also applicable in the arc discharge processing.

When the sublimation process is performed by irradiating with laser orelectron beam, preferably pelletized metal tungsten or tungsten compoundis used as the raw material. The laser or electron beam has a smallirradiation spot diameter, and thus supply becomes difficult when themetal tungsten powder or the tungsten compound powder is used. However,using the pelletized metal tungsten or tungsten compound makes itpossible to perform sublimation efficiently. The laser may be one havingsufficient energy for sublimating the metal tungsten or the tungstencompound and is not particularly limited, but CO₂ laser is preferredbecause of its high energy.

When the pellets are irradiated with the laser or electron beam, movingat least one of the irradiation source of the laser light or electronbeam and the pellets enables to effectively sublimate the entire surfaceof a pellet having a certain degree of size. This makes it easy toobtain the tungsten trioxide powder having a crystal structure in whichrhombic crystal is mixed with at least one selected from monocliniccrystal and triclinic crystal. The pellets as described above are alsoapplicable in the inductively coupled plasma processing and the arcdischarge processing.

The tungsten oxide based particles used for the aqueous dispersionliquid of this embodiment can be obtained just by the sublimationprocess as described above, but it is also effective to perform heattreatment process on the tungsten oxide based particles produced in thesublimation process. The heat treatment process is to heat treat thetungsten trioxide based particles obtained in the sublimation process atpredetermined temperatures and for predetermined time in an oxidativeatmosphere. Also in the case where the tungsten trioxide particlescannot be formed sufficiently by condition control or the like in thesublimation process, the percentage of the tungsten trioxide particlesin the tungsten oxide particles can be 99% or more, substantially 100%,by performing the heat treatment. Moreover, the crystal structure of thetungsten trioxide particles can be adjusted to a predetermined structurein the heat treatment process.

Examples of the oxidative atmosphere used in the heat treatment processinclude air and oxygen-containing gas. The oxygen-containing gas meansinert gas containing oxygen. It is preferred that the heat treatmenttemperature be in the range of 200° C. to 1000° C., more preferably 400°C. to 700° C. It is preferred that the heat treatment time be in therange of 10 minutes to 5 hours, more preferably 30 minutes to 2 hours.By having the temperature and time of the heat treatment process in theabove-described ranges, the tungsten trioxide can be formed easily fromtungsten oxide other than the tungsten trioxide. Further, to obtain apowder with less defects and good crystallinity, it is preferred thattemperature increase or temperature decrease during heat treatment beperformed gradually. Rapid heating or cooling during heat treatmentleads to decrease of crystallinity.

When the heat treatment temperature is lower than 200° C., it ispossible that an oxidation effect for turning a powder which did notbecome the tungsten trioxide in the sublimation process to the tungstentrioxide is not obtained sufficiently. When the heat treatmenttemperature is higher than 1000° C., the tungsten oxide particles growrapidly, and thus the specific surface area of the obtained finetungsten oxide powder can decrease easily. Moreover, by performing theheat treatment process at the temperatures and for the time as describedabove, it is possible to adjust the crystal structure and crystallinityof the fine tungsten trioxide powder.

The aqueous dispersion liquid in this embodiment can be used as a filmforming material in the state as it is. The aqueous dispersion liquid ismixed with a binder component or the like to produce a coating material,and this coating material may be used as a film forming material. Thecoating material contains at least one binder component selected from aninorganic binder and an organic binder together with the aqueousdispersion liquid. It is preferred that the content of the bindercomponent be in the range of 5 mass % to 95 mass %. When the content ofthe binder component is more than 95 mass %, it is possible that desiredphotocatalytic performance cannot be obtained. When the content of thebinder component is less than 5 mass %, sufficient coupling force cannotbe obtained, and the film characteristics may decrease. By applying sucha coating material, strength, hardness, adhesion strength to thesubstrate, and the like of the film can be adjusted to a desired state.

As the organic binder, for example, there is used a product obtained bydecomposing a hydrolytic silicon compound such as an alkyl silicate, asilicon halide, and a partial hydrolytic product of them, an organicpolysiloxane compound or a polycondensate thereof, silica, colloidalsilica, water glass, a silicon compound, phosphate such as zincphosphate, metal oxide such as zinc oxide or zirconium oxide, densephosphate, cement, gypsum, lime, frit for enamel, or the like. As theorganic binder, for example, there is used fluorine based resin,silicone resin, acrylic resin, epoxy resin, polyester resin, melamineresin, urethane resin, alkyd resin, or the like.

By applying the aqueous dispersion liquid or the coating material asdescribed above on the substrate, a film containing the tungsten oxidebased particles can be formed stably and uniformly. As the substrate onwhich such a film is formed, a glass, a ceramic, a plastic, a resin suchas acrylic resin, a paper, a fiber, a metal, a wood, or the like isused. It is preferred that the film thickness be in the range of 2 nm to1000 nm. When the film thickness is smaller than 2 nm, it is possiblethat the state that the tungsten oxide based particles exist uniformlyis not obtained. When the film thickness is larger than 1000 nm,adhesion strength to the substrate decreases. It is preferred that thefilm thickness be in the range of 2 nm to 400 nm.

It is preferred that the film of this embodiment have the photocatalyticperformance under irradiation with visible light. Generally, the visiblelight is light having a wavelength in the region of 380 nm to 830 nm,and is light irradiated from a general illumination, such as a whitefluorescent light, sunlight, a white LED, an electric bulb, a halogenlamp, or a xenon lamp, or a blue light emitting diode, a blue laser, orthe like as a light source. The film in this embodiment exhibits thephotocatalytic performance in an ordinary indoor environment. Thephotocatalytic performance is an operation such that upon absorption oflight, a pair of electron and positive hole is excited with respect toone photon, and the excited electron and positive hole activate hydroxylor acid at the surface by oxidation-reduction, and an active oxygenspecies generated by this activation oxidatively decomposes organic gasand the like, and is further an operation to exhibit hydrophilicity,antibacterial/disinfection performance, and the like.

A product of this embodiment includes a film formed using the aqueousdispersion liquid or the coating material described above. Specifically,the film is formed by applying the aqueous dispersion liquid or thecoating material on the surface of the substrate constituting theproduct. The film formed on the substrate surface may contain a zeolite,an activated carbon, a porous ceramic, or the like. The photocatalystfilm described above and the product including this film arecharacterized in that they excel in decomposing performance for organicgas such as acetaldehyde and formaldehyde under irradiation with visiblelight, and especially exhibit high activity even under low illuminance.The film of this embodiment exhibits hydrophilicity by contact anglemeasurement with water. Moreover, the film exhibits high antibacterialperformance in antibacterial performance estimation againststaphylococcus aureus bacteria or colon bacillus under irradiation withvisible light.

Specific examples of the product including the film of this embodimentinclude air-conditioners, air cleaning devices, electric fans,refrigerators, microwave ovens, dishwasher/driers, rice cookers, pots,pot lids, IH heaters, washing machines, vacuum cleaners, lightingapparatuses (lamps, apparatus bodies, shades, and the like), sanitaryproducts, toilets, washbowls, mirrors, bathrooms (walls, ceilings,floors, and the like), building materials (interior walls, ceilingmaterials, floors, exterior walls, and the like), interior products(curtains, carpets, tables, chairs, sofas, shelves, beds, beddings, andthe like), glasses, sashes, hand rails, doors, knobs, clothes, filtersused for home electric appliance or the like, stationery, kitchenutensils, members used in the inside space of a car, and the like. Whenthe tungsten oxide based particles have the photocatalytic performance,the photocatalyst effect can be given to the product. Examples of thesubstrate to be applied include a glass, a ceramic, a plastic, a resinsuch as acrylic resin, a paper, a fiber, a metal, a wood, and the like.

When a fiber is used as the substrate, as a fiber material there is useda synthetic fiber such as polyester, nylon, or acrylic fiber, aregenerated fiber such as rayon, a natural fiber such as cotton, wool,or silk, a combined fiber, a union cloth, a blended fiber of them, orthe like. The fiber material may be in a loose fiber form. The fiber mayhave any form such as textile, knitting, or nonwoven fabric, or may beone on which ordinary dyeing or printing is performed. When the aqueousdispersion liquid is applied to the fiber material, a useful method isto use the tungsten oxide based particles together with a resin binderfor fixing it to the fiber material.

As the resin binder, a resin of water soluble type, water dispersibletype, or solvent soluble type can be used. Specifically, a melamineresin, an epoxy resin, a urethane resin, an acrylic resin, afluorocarbon resin, or the like is used, but it is not limited to them.When the tungsten oxide based particles are fixed to the fiber materialusing the aqueous dispersion liquid, for example, the aqueous dispersionliquid is mixed with a resin binder of water dispersible type or watersoluble type to produce a resin liquid, and the fiber material is dippedin this resin liquid and is thereafter wringed by a mangle roller anddried. By thickening the resin liquid, it can be coated on one side ofthe fiber material with a publicly known apparatus such as a knifecoater. It is also possible to use a gravure roller to make the tungstenoxide based particles adhere to one side or both sides of the fibermaterial.

When the tungsten oxide based particles are made to adhere to the fibersurface using the aqueous dispersion liquid, if the adhering amount istoo small, it is not possible for the tungsten oxide based particles tosufficiently exhibit the gas decomposing performance and theantibacterial performance which they have. If the adhering amount is toolarge, the performance which the tungsten oxide based particles have isexhibited, but the aesthetic property as the fiber material maydecrease. Accordingly, preferably an appropriate adhesion amount isselected depending on the material or application. When the tungstenoxide based particles contained in the aqueous dispersion liquid havethe photocatalytic performance under irradiation with visible light,clothes and interior goods using a fiber with the tungsten oxide basedparticles adhering on its surface is capable of exhibiting an excellentodor eliminating effect and antibacterial effect under irradiation withvisible light in an indoor environment.

As described above, also when the dispersion agent is not used, theaqueous dispersion liquid of this embodiment excels in dispersibility ofthe tungsten oxide based particles. Thus, the tungsten oxide basedparticles do not precipitate for a long time, and stable liquidity canbe maintained. Therefore, using the aqueous dispersion liquid or thecoating material as such enables to provide a uniform and smooth film,and a product having such a film. Moreover, when the tungsten oxidebased particles having the photocatalytic performance are used, itbecomes possible to provide a photocatalyst film having photocatalyticperformance such as excellent organic gas decomposing performance,hydrophilicity, antibacterial/disinfection performance, and the like,and further a product having this film.

EXAMPLES

Next, specific examples will be described. Note that in the examplesbelow, as a method of producing a powder, there is used a methodapplying inductively coupled plasma processing in the sublimationprocess, but it is not limited to this method.

Example 1

First, the tungsten trioxide powder with a mean particle diameter of 0.5vim was prepared as a raw material powder. This raw material powder wassprayed with carrier gas (Ar) on RF plasma, and further, as reactiongas, argon was supplied at a flow rate of 40 L/min and oxygen at a flowrate of 40 L/min. In this manner, the sublimation process of subjectingthe raw material powder to oxidation reaction while sublimating it wascarried out to produce a tungsten oxide powder. The tungsten oxidepowder was heat treated under conditions of 900° C.×1.5 h in theatmosphere.

The mean primary particle diameter (D50) and the BET specific surfacearea of the tungsten oxide powder were measured. The mean primaryparticle diameter was measured by image analysis of a TEN picture. ForTEM observation, H-7100FA made by Hitachi was used, an enlarged picturewas subjected to image analysis and 50 particles or more were extracted,and integrated diameters with reference to volumes were obtained tocalculate the D50. Measurement of the BET specific surface area wasperformed using a specific surface area measuring apparatus Macsorb 1201made by Mountech. Preprocessing was carried out under conditions of 200°C.×20 minutes in nitrogen. Measurement results of the mean primaryparticle diameter (D50) and the BET specific surface area are shown inTable 1.

Next, the aqueous dispersion liquid was produced using the obtainedtungsten oxide powder. The tungsten oxide powder was dispersed in waterso that the concentration thereof becomes 10 mass %. Adjustment was madeusing water, sulfuric acid, and TMAH so that the pH of the dispersionwater becomes 4.5. The dispersion processing was carried out using abeads mill. Measurement results of concentration and pH of the thusproduced aqueous dispersion liquid are shown in Table 1.

Dispersibility of the aqueous dispersion liquid was estimated. Theestimation of dispersibility was carried out just after the dispersionliquid was produced and after the liquid was left for two months. Thedispersibility was estimated based on the D90 diameter of a particlesize distribution and visual check of a precipitation state. Resultsthereof are shown in Table 2. The D90 diameter of the particle sizedistribution was measured using Microtrack MT3300 (laser diffractionparticle size distribution analyzer) made by Nikkiso. When the maximumparticle diameter is 6 μm or smaller, measurement was performed usingNanotrack UPA-EX made by Nikkiso. Also in this case, substantiallyequivalent data were obtained. The visual state check was evaluatedbased on the presence of precipitated particles. Results of the visualobservation are shown in Table 2 as (D) when particles are precipitated,(C) when particles are precipitated slightly, (B) when no particles areprecipitated, and (A) when no particles are precipitated and there is nodifference in concentration between an upper and lower portions.

Example 2

The tungsten oxide powder was produced through the sublimation processsimilar to that of Example 1 except that oxygen is supplied at a flowrate of 80 L/min as reaction gas, and the pressure in the reactioncontainer is adjusted to 25 kPa that is the decompression side. Further,using the obtained tungsten oxide powder, the aqueous dispersion liquidwas produced similarly to Example 1. Measurement and evaluation similarto those in Example 1 were performed on the tungsten oxide powder andthe aqueous dispersion liquid. Powder properties and dispersion liquidproperties are shown in Tablet. Moreover, stability of the aqueousdispersion liquid was measured and evaluated similarly to Example 1.Evaluation results are shown in Table 2.

Example 3

The tungsten oxide powder was produced similarly to Example 1 exceptthat heat treatment of the tungsten oxide powder is performed underconditions of 500° C.×2 h in the atmosphere. Next, using the obtainedtungsten oxide powder, the aqueous dispersion liquid was producedsimilarly to Example 1. Properties of the tungsten oxide powder and theaqueous dispersion liquid are shown in Table 1. Moreover, stability ofthe aqueous dispersion liquid was measured and evaluated similarly toExample 1. Evaluation results are shown in Table 2.

Examples 4 to 14

In Example 4, the dispersion processing of the tungsten oxide powder inExample 2 was performed under conditions which cause the D90 diameter tobe small, so as to produce the aqueous dispersion liquid. In Examples 5to 7, the aqueous dispersion liquid was produced using the tungstenoxide powder of Example 3 while adjusting its concentration to be in therange of 0.5 mass % to 20 mass %. In Example 8, the aqueous dispersionliquid was produced using the tungsten oxide powder produced similarlyto Example 1 except that heat treatment is performed under conditions of850° C.×1.5 h in the atmosphere. In Examples 9 and 10, the aqueousdispersion liquid was produced similarly to Example 6 except that theadjustment value of pH is changed.

In Example 11, the aqueous dispersion liquid was produced similarly toExample 6 except that a raw material containing a large amount of Fe andMo is used as the raw material powder in the sublimation process. Thecontent of Fe in the tungsten oxide composite powder was 300 ppm. InExample 12, the aqueous dispersion liquid was produced similarly toExample 6 except that zirconium oxide powder is mixed in the rawmaterial powder to be used in the sublimation process. The content of Zrin the tungsten oxide composite powder was 1000 ppm. In Example 13, theaqueous dispersion liquid was produced similarly to Example 6 exceptthat platinum powder is mixed in the raw material powder to be used inthe sublimation process. The content of Pt in the tungsten oxidecomposite powder was 1000 ppm. In Example 14, the aqueous dispersionliquid was produced similarly to Example 6 except that water containing10 mass % of alcohol is used as the dispersion medium.

Dispersion stability of the aqueous dispersion liquids of Examples 4 to14 was measured and evaluated similarly to Example 1. Results thereofare shown in Table 2.

As is clear from Table 2, in the aqueous dispersion liquids of Examples1 to 3, there were ones with a relatively large D90 diameter based onthe dispersion conditions, and slight precipitation was recognized inthe dispersion liquids. However, after two months, they changed slightlyand were relatively stable. All the aqueous dispersion liquids ofExamples 4 to 14 had a small D90 diameter, and exhibited good propertieswhile having no precipitation. Moreover, almost no precipitationoccurred after two months and there were small changes in particlediameters, and thus excellent stability was recognized. These dispersionliquids exhibited similar states after it was stored for three months,and it was recognized that they are stable for a long period. Inaddition, when the adjustment range of pH is close to strongly acidicside or neutral, the liquids were relatively uniform and stable justafter the dispersion, but precipitation was seen, although it was small,after two months.

Comparative Example 1

An aqueous dispersion liquid was produced under conditions similar tothose of Example 6 except that the adjustment range of pH is changed tothe strongly acidic side. The pH of the aqueous dispersion liquid was0.5, and slight precipitation was seen just after dispersion. After itwas stored for two months, the precipitation advanced further and theprecipitation amount increased. It is conceivably due to that the zetapotential became close to zero and it became liable to precipitate.

Comparative Example 2

A dispersion liquid was produced under conditions similar to those ofExample 6 except that the concentration of the tungsten oxide powder is50 mass % and the adjustment range of pH is changed to be close to thevicinity of neutral. The pH of the aqueous dispersion liquid was 7.1,and the tungsten oxide dissolved.

Comparative Example 3

A tungsten oxide powder which is commercially available (made byRaremetallic) as a reagent was used to produce an aqueous dispersionliquid having concentration of 10 mass % and pH of 5.2. The particlediameter of the tungsten oxide powder is too large and hence it does notdisperse in water sufficiently, and it was recognized that there islarge precipitation.

TABLE 1 POWDER PROPERTIES DISPERSION MEAN BET LIQUID PARTICLE SPECIFICPROPERTIES DIAMETER SURFACE CONCEN- (D50) AREA TRATION [nm] [m²/g] [MASS%] pH EXAMPLE 1 195 3.9 10 4.5 EXAMPLE 2 4 201 10 3.8 EXAMPLE 3 25 35 104.2 EXAMPLE 4 4 201 10 4.5 EXAMPLE 5 25 35 0.5 4.5 EXAMPLE 6 25 35 104.0 EXAMPLE 7 25 35 20 3.4 EXAMPLE 8 95 8.5 10 4.0 EXAMPLE 9 25 35 102.2 EXAMPLE 10 25 35 10 6.4 EXAMPLE 11 25 35 10 4.2 EXAMPLE 12 25 36 104.1 EXAMPLE 13 25 35 10 4.0 EXAMPLE 14 25 35 10 3.4 COMPARATIVE EXAMPLE1 25 35 10 0.5 COMPARATIVE EXAMPLE 2 25 35 50 7.1 COMPARATIVE EXAMPLE 31210 0.7 10 5.2

TABLE 2 DISPERSION STABILITY OF DISPERSION LIQUIDS (CONTACT ANGLEMEASUREMENT RESULTS) JUST AFTER AFTER DISPERSION 2 MONTHS VISUAL VISUALD90 EVALU- D90 EVALU- [nm] ATION* [nm] ATION* EXAMPLE 1 15 (C) 16 (D)EXAMPLE 2 12 (C) 13 (D) EXAMPLE 3 0.110 (A) 0.130 (A) EXAMPLE 4 0.085(A) 0.090 (A) EXAMPLE 5 0.090 (A) 0.091 (A) EXAMPLE 6 0.097 (A) 0.098(A) EXAMPLE 7 0.100 (A) 0.100 (A) EXAMPLE 8 0.950 (A) 0.965 (A) EXAMPLE9 0.099 (B) 0.110 (C) EXAMPLE 10 0.089 (B) 0.095 (B) EXAMPLE 11 0.097(A) 0.100 (A) EXAMPLE 12 0.095 (A) 0.102 (A) EXAMPLE 13 0.090 (A) 0.099(A) EXAMPLE 14 0.099 (A) 0.103 (A) COMPARATIVE 0.240 (C) 0.420 (D)EXAMPLE 1 COMPARATIVE — DISSOLVED — — EXAMPLE 2 COMPARATIVE 65 (D) 66(D) EXAMPLE 3 *(A): NO PRECIPITATION, NO CONCENTRATION DIFFERENCEBETWEEN UPPER AND LOWER PORTIONS (B): NO PRECIPITATION (C): SLIGHTLYPRECIPITATED (D): PRECIPITATED

Example 15

In the aqueous dispersion liquid obtained in Example 6, 1 mass % ofcolloidal silica was mixed with the tungsten oxide powder to produce awater based coating material. Dispersibility of this coating materialwas evaluated just after it was produced and after it was stored for twomonths. Results thereof are shown in Table 3. The water based coatingmaterial of Example 15 is a uniform dispersion liquid with noprecipitation of particles similarly to the aqueous dispersion liquid,and it was recognized that it is stable even when it is stored for along period.

Comparative Example 4

Dispersibility of a coating material including a commercially availabletitanium oxide was evaluated when it was purchased and after it wasstored for two months. Results thereof are shown in Table 3. In thecommercially available coating material, a time already elapsed fromproduction, and slight precipitation of particles was recognized.Further, after it was stored for two months, aggregation advanced andprecipitated particles increased.

TABLE 3 DISPERSION STABILITY OF DISPERSION LIQUIDS (CONTACT ANGLEMEASUREMENT RESULTS) JUST AFTER AFTER DISPERSION 2 MONTHS VISUAL VISUALD90 EVALU- D90 EVALU- [nm] ATION* [nm] ATION* EXAMPLE 15 0.115 (A) 0.120(A) EXAMPLE 4 0.110 (C) 0.180 (D)

Example 16

The water based coating material of Example 15 was applied on thesurface of a glass and dried to thereby produce a glass having atungsten oxide coating layer on its surface. On the surface of thisglass, presence of rough particles and aggregated particles was checkedvisually, but no existence of rough particles and aggregated particleswas recognized. It was recognized that a uniform film is obtained.Moreover, when arbitrary portions were observed via a microscope, it wasrecognized that an even film was formed in each portion.

Example 17

A photocatalyst film was formed on a glass surface using the aqueousdispersion liquid of Example 6. The photocatalytic performance of thisphotocatalyst film under irradiation with visible light was evaluated.The photocatalytic performance was evaluated by measuring adecomposition rate for acetaldehyde gas. Specifically, a distributiontype apparatus similar to the one for removal performance (decomposingperformance) evaluation for nitrogen oxide of JIS-R-1701-1 (2004) wasused to measure the gas decomposition rate under conditions describedbelow. Moreover, when it is represented by the L*a*b color system, theaqueous dispersion liquid had a color with a* of −14, b* of 15, and L*of 80. The aqueous dispersion liquid as such attains the photocatalyticperformance when being applied on a substrate, but does not impair thecolor of the substrate.

A decomposition test for acetaldehyde gas was performed as follows. Theinitial concentration of acetaldehyde is 10 ppm, the gas flow rate is140 mL/min, and a sample amount is 0.2 g. The sample is adjusted suchthat it is applied on a glass plate of 5 cm×10 cm and dried.Preprocessing is irradiation with black light for 12 hours. A whitefluorescent light (FL20SS W/18, made by Toshiba Lighting & Technology)is used as a light source, and an ultraviolet cutting filter (KralexN-169, made by Nitto Jushi Kogyo) is used to cut wavelengths under 380nm. Illuminance is adjusted to 1000 lx. First, irradiation with light isnot performed, and it is waited until gas absorption ceases and the gasbecomes stable. Irradiation with light is started after it becomesstable. Under such conditions, irradiation with light is performed, thegas concentration after 15 minutes elapses is measured, and a gasdecomposition rate is obtained. However, when the gas concentration doesnot become stable even after 15 minutes elapse, the concentration ismeasured continuously until it becomes stable.

The gas concentration before the light irradiation is denoted by A, thegas concentration when 15 minutes elapse from the light irradiation andit becomes stable is denoted by B, and a value calculated based on[Formula: (A−B)/A×100] from these gas concentration A and gasconcentration B is assumed as the gas decomposition rate (%). As the gasanalyzing apparatus, Multi-gas Monitor 1412 made by INOVA was used. As aresult of performing such measurement, it was recognized that thephotocatalytic performance is stably exhibited. This is because theproduced tungsten oxide powder itself has the photocatalyticperformance, and by performing the dispersion processing underconditions which do not cause decrease in activity of the powder, it ispossible to exhibit the photocatalytic performance even in a dispersionliquid and a coating material.

Example 18

The aqueous dispersion liquid of Example 6 was mixed with a resin liquidof acrylic resin, and a plain weave fabric formed of polyester weighing150 g/m² was dipped in this mixed liquid (coating material), so as toproduce a polyester fiber to which the tungsten oxide photocatalyst isadhered. A sample of 5 cm×10 cm was cut from each of the fiber to whichthe photocatalyst is adhered and a fiber to which no photocatalyst isadhered, and the photocatalytic performance under irradiation withvisible light was evaluated with each of them by a method similar tothat in Example 17. As a result, it was recognized that the polyesterfiber to which the photocatalyst is adhered is higher in decompositionrate for acetaldehyde gas than the fiber to which it is not adhered.Further, 10 similarly produced samples were prepared and dispersion inperformance was evaluated, and it was recognized that the adhesionamount of the photocatalyst to the fiber is stable since the dispersionliquid of this example has excellent dispersibility. Further, it wasrecognized that the polyester fiber retains a uniform aestheticproperty.

Example 19

The aqueous dispersion liquid with pH 4 produced in Example 6 wasapplied on a silicon substrate, and dried under conditions of 150° C.×10minutes, so as to produce a film. Existence of surface hydroxyl waschecked by a transmission method with FT-IR (Fourier-transform infraredabsorption spectroscopy/apparatus name: IFS66v made by BRUKER), and apeak originated in hydroxyl in the vicinity of 3700 cm⁻¹ was recognized.Moreover, the dispersion liquid was applied on the glass substrate (5cm×10 cm), and dried under conditions of 150° C.×10 minutes, so as toproduce a film with an adhesion amount of the tungsten oxide of 0.1 g/50cm². The photocatalytic performance of this film was evaluated by amethod similar to that in Example 17. A preprocessing by black light wasperformed for one hour, and the irradiation intensity of the visiblelight was 6000 lx. The gas decomposition rate was 80.1%.

Further, the zeta potential of the dispersion liquid was measured. Formeasuring the zeta potential, ELSZ-2 and pH Titrator System (ELSZ-PT)made by Otsuka Electronics were used. As pH adjusters, an HCl aqueoussolution of 0.1 mol/L was used for adjusting acidity, and NaOH of 0.1mol/L was used for adjusting alkalinity. The dispersion liquid dilutedto 0.1 mass % is adjusted to pH 2, 3, 4, 5, 6, and 7 by the pH Titrator,and thereafter the zeta potential was measured with each pH. The zetapotential with pH 4 was −29.9 mV. Results thereof are shown in Table 4.

Example 20

The pH of the aqueous dispersion liquid obtained in Example 6 wasadjusted by TMAH, so as to produce a dispersion liquid with pH 6. Thisdispersion liquid was applied on a silicon substrate and dried underconditions of 150° C.×10 minutes, so as to produce a film. Similarly toExample 19, existence of surface hydroxyl was checked with the FT-IR,and it was recognized that a peak originated in hydroxyl in the vicinityof 3700 cm⁻¹ is largely decreased. Moreover, the decomposition rate foracetaldehyde gas was measured similarly to Example 19 using thedispersion liquid adjusted to pH 6, and the gas decomposition rate was54%. The zeta potential with pH 6 was −32.3 mV. Results thereof areshown in Table 4. It is conceivable that hydroxyl on the surfaces of thetungsten oxide particles decreases by adjusting the pH to 6, anddecrease of the gas decomposition rate occurs.

Example 21

The pH of the aqueous dispersion liquid obtained in Example 6 wasadjusted with sulfuric acid, so as to produce a dispersion liquid withpH 2. The dispersion liquid was applied on a silicon substrate and driedunder conditions of 150° C.×10 minutes, so as to produce a film.Similarly to Example 19, existence of surface hydroxyl was checked withthe FT-IR, and a peak originated in hydroxyl in the vicinity of 3700cm⁻¹ was recognized. Moreover, the decomposition rate for acetaldehydegas was measured similarly to Example 19 using the dispersion liquidadjusted to pH 2, and the gas decomposition rate was 61.1%. The zetapotential with pH 2 was −7.9 mV. Results thereof are shown in Table 4.By adjusting to pH 2, the zeta potential in the aqueous dispersionliquid was decreased. Accordingly, the particles tend to aggregate. Itis conceivable that the specific surface area decreases by aggregationof the particles, and thus decrease of the gas decomposition rateoccurs.

TABLE 4 FILM PROPERTIES FTIR GAS ZETA DISPERSION PEAK DECOM- POTEN-LIQUID NEAR POSITION TIAL pH 3700 cm⁻¹ RATE (%) (mV) EXAMPLE 19 4 (B)80.1 −29.9 EXAMPLE 20 6 (D) 54.0 −32.3 EXAMPLE 21 2 (B) 61.1 −7.9

Example 22

The coating material produced in Example 15 was applied on a glass ofthe interior space of an automobile to form a photocatalyst film, andthis caused decrease in cigarette odor and prevented the glass frombeing soiled easily. Incidentally, when hydrophilicity of the glass onwhich this coating material is applied was evaluated, the contact anglewas 1° or smaller, and superhydrophilicity was exhibited. Moreover,evaluation of antibacterial performance was performed using aureusbacteria, colon bacillus, and mold, and it was recognized that excellentantibacterial performance is exhibited against all of them.

The aqueous dispersion liquids using the tungsten oxide based particlesof the above-described respective examples have excellentdispersibility, and hence are capable of providing a uniform film. Sincethe tungsten oxide based particles have the photocatalytic performance,the decomposing performance for organic gas such as acetaldehyde can beobtained stably, and moreover, visual problems of color unevenness andthe like do not occur easily. Thus, the liquids can be used preferablyfor members used in the interior space of an automobile, buildingmaterials and interior materials used in factories, shops, schools,public facilities, hospitals, welfare facilities, accommodations,houses, and the like, and home electronic appliances, and the like.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and sprit of the inventions.

1. An aqueous dispersion liquid comprising particles selected fromtungsten oxide particles and tungsten oxide composite particles and adispersion medium including water, wherein a mean primary particlediameter (D50) of the particles is in a range of 1 nm to 400 nm, aconcentration of the particles in the aqueous dispersion liquid is in arange of 0.1 mass % to 40 mass %, and pH of the aqueous dispersionliquid is in a range of 1.5 to 6.5, and wherein the tungsten oxidecomposite contains at least one metal element selected from transitionmetal elements and aluminum, or a compound including at least one metalelement selected from transition metal elements and aluminum, in a rangeof 0.001 mass % to 50 mass % as an amount of the metal element, balancedby tungsten oxide.
 2. The aqueous dispersion liquid according to claim1, wherein the concentration of the particles is in a range of 1.0 mass% to 20 mass %, and pH is in a range of 2.5 to 5.5.
 3. The aqueousdispersion liquid according to claim 1, wherein a BET specific surfacearea of the particles is in a range of 4.1 m²/g to 820 m²/g.
 4. Theaqueous dispersion liquid according to claim 1, wherein a D90 diameterof a particle size distribution of the particles in the aqueousdispersion liquid is in a range of 0.01 μm to 10 μm.
 5. The aqueousdispersion liquid according to claim 1, wherein the metal element is atleast one element selected from titanium, zirconium, manganese, iron,palladium, platinum, copper, silver, aluminum, and cerium.
 6. Theaqueous dispersion liquid according to claim 1, wherein the dispersionmedium further comprises alcohol in a range of 20 mass % or less.
 7. Acoating material comprising: the aqueous dispersion liquid according toclaim 1; and at least one binder component selected from an inorganicbinder and an organic binder.
 8. The aqueous dispersion liquid accordingto claim 1, wherein the tungsten oxide composite contains the metalelement or the compound in a range of 0.01 mass % to 10 mass % as theamount of the metal element.
 9. The aqueous dispersion liquid accordingto claim 1, wherein the compound is an oxide of the metal element.